A half-day here means three to four hours and two stops: Carthage, then Sidi Bou Said. What gets dropped is the Medina of Tunis, the lunch stop and, on most listings, the Bardo. Whether that is a real loss depends almost entirely on where you are staying.
From Tunis, a half-day is a half-day
Carthage is twenty minutes from central Tunis. A four-hour tour gives you roughly two hours at the ruins and one in the village, and hands the afternoon back. The guided half-day from Tunis includes the entry fees and a guide, and covers Byrsa Hill, the Carthage National Museum, the Punic ports and the Tophet before finishing on the cliff at Sidi Bou Said.
That is a genuinely efficient use of a morning, and it is why the Tunis half-days command a higher price than some eight-hour resort excursions.
From Hammamet, the arithmetic changes
The half-day from Hammamet is listed at three to six hours, and the range is honest: from Tunis it is genuinely short, and from Hammamet an hour and a half of driving at each end turns it into most of a day anyway.
What it does keep is the thing the full-day resort coaches often lose. The operator states explicitly that there are no shopping detours and no commercial stops, which on a Tunisian excursion is worth reading twice. A carpet showroom on the way home is standard practice and can absorb an hour.
What a half-day cannot do
It cannot give Carthage more than an hour or two, and it cannot add the medina. If you want the souks, the lunch and the Bardo, you want the full-day options instead.
It also usually excludes the Carthage entry ticket on the cheaper listings. Budget roughly 30 dinars a head at the gate, in cash. Our tickets guide has the detail.
The village-only variant
If the ruins are not the draw, there is a half-day transfer to Sidi Bou Said alone from the Hammamet coast at around $24, giving you two hours in the village and nothing else. A hundred reviews say it does what it promises, and there is a sunset departure if photographs are the point. Our honest assessment of whether Sidi Bou Said is worth it covers when to go.
The other direction: Carthage only
The mirror image also exists. A three-hour walking tour of Carthage covers seven sites on foot with a licensed guide and every ticket included, and skips Sidi Bou Said entirely. It starts near Salammbo station, reachable on the TGM from Tunis for well under a dinar, and at 4.8 from 46 reviews it is the deepest look at the ruins available in half a day.
You can, of course, do both: the walking tour in the morning, then one TGM stop up the line to the village in the afternoon.
Check availability for your dates.